106 ASAIO Journal 2014 In this study, we have demonstrated the ability of cord blood (CB)-derived unrestricted somatic stem cells (USSCs) and chitosan-modified poly(3-hydroxybutyrate-co-3-hydroxyval- erate) (PHBV) scaffold to promote skin regeneration. After- ward, the scaffolds were evaluated by structural, microscopic, physical, and mechanical assays and cell culture analyses. Results of structural, physical, and mechanical analyses also showed a good resilience and compliance with movement as a skin graft. Cellular experiments showed a better cell adhe- sion, growth, and proliferation inside the modified scaffolds compared with unmodified ones. In animal models with histo- logical examinations, all groups, excluding the control group especially the groups treated with stem cells, exhibited the most pronounced effect on wound closure, with the statisti- cally significant improvement in wound healing being seen at postoperative day 21. These data suggest that chitosan-modi- fied PHBV scaffold loaded with CB-derived USSCs could sig- nificantly contribute to wound repair and be potentially used in the tissue engineering. ASAIO Journal 2014; 60:106–114. Key Words: porous PHBV scaffold, chitosan, unrestricted somatic stem cells, wound healing, histological assessments The prognosis for extensive and deep skin injury is not satis- factory because of scar formation and the loss of normal func- tion and skin appendages. Several novel therapies for skin repair and regeneration have emerged. Stem cell–based therapies are attractive candidates in regenerative medicine to treat skin inju- ries, such as chronic wounds and radiolesions. Stem cell ther- apy has emerged as a promising new approach in almost every medicine specialty. It has been demonstrated that mesenchymal stem cells (MSCs) play an effective role in promoting wound healing when injected into the skin defects, either alone or in combination with scaffold. 1,2 Umbilical cord blood (CB) con- tains hematopoietic as well as nonhematopoietic MSCs, these latter also named as CB embryonic–like stem cells. 3 Umbilical cord MSCs have become a unique, accessible, and noncon- troversial source of regeneration in medicine. 4,5 Cord blood embryonic–like stem cells have been shown to differentiate into neural, hepatobiliary, pancreatic-like precursors, and potentially to the other ones. 3,6 Unrestricted somatic stem cells (USSCs) from umbilical cord blood (UCB) isolated by Jager and his colleagues and evaluated the differentiation capacity and cytokine produc- tion of these cells for transplantation. In fact, USSCs are one of the rare cell populations in UCB which are considered pluripo- tent. Human UCB-derived USSCs have previously been demon- strated to have a broad differentiation potential and regenerative beneficial effects when administered in animal models of mul- tiple degenerative diseases. 7 It was also suggested that stem cells from UCB are able to differentiate into epithelial cells under in vitro conditions and could therefore be used as a starting mate- rial for isolation and expansion of cells in large skin defects. 8 Tissue regeneration is a process aided by cellular sciences, engi- neering, and medicine to repair defected tissues and restore their functions. 9 One of the key factors of tissue engineering is to create a three-dimensional scaffold with suitable properties also, degradation rate, high porosity, interconnected pores, etc. Wide variety of natural materials, such as collagen (Biobrane, Integra, Alloderm), fibrin (Bioseed), HA (Laserskin), and GAGs (Integra), have been used in commercialized skin grafts. 10–12 Nylon (Tran- scyte) and biodegradable polymers, such as polyglactin (Der- mgraft), polycaprolactone, 13 and poly(lactic-co-glycolic acid) (PLGA) 14 were used for fabricating skin substitutes. Polyhydoxy- alkanoates are polyesters produced by microorganisms under unbalanced growth conditions. Polyhydoxyalkanoates are gen- erally biodegradable, with good biocompatibility, making them attractive as tissue engineering biomaterials. 15–25 It is well-known that the chitosan is a natural biomaterial derived from the chitin. It is found in the shells of crustaceans, such as lobsters, crabs, and shrimp, and many other organisms, including insects and fungi. Chitosan is a linear polysaccharide composed of randomly dis- tributed β-(1–4)-linked D-glucosamine (deacetylated unit) and N-acetyl-D-glucosamine (acetylated unit). It has a number of commercial and possible biomedical applications especially for skin regeneration. 26 Controlling the biomaterials surface prop- erties is essential for the high performance of cell adhesion. Wettability is an important factor in the surface modification of biomaterials. Modification of hydrophobic polymer surfaces can be achieved by wet (acid, alkali), dry (plasma), radiation treat- ments (ultraviolet radiation and laser), and chemical methods like cross-linking. 18,27,28 Tissue Engineering\Biomaterials Regeneration of Full-Thickness Skin Defects Using Umbilical Cord Blood Stem Cells Loaded into Modified Porous Scaffolds REZA ZEINALI,* ESMAEIL BIAZAR,† SAEED HEIDARI KESHEL,‡§ MOSTAFA REZAEI TAVIRANI,‡ AND KAMAL ASADIPOUR* Copyright © 2013 by the American Society for Artificial Internal Organs DOI: 10.1097/MAT.0000000000000025 From the * Department of Biomedical Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran; † Department of Biomaterial Engineering, Tonekabon Branch, Islamic Azad Univer- sity, Tonekabon, Iran; ‡ Proteomics Research Center, Shahid Beheshti University of Medical Science, Tehran, Iran; and § Tissue Engineering Department, School of Advanced Technologies in Medicine, Tehran University of Medical Science, Tehran, Iran. Submitted for consideration August 2013; accepted for publication in revised form September 2013. Disclosure: The authors have no conflicts of interest to report. Reprint Requests: Esmaeil Biazar, Department of Biomedical Engi- neering, Tonekabon Branch, Islamic Azad University, Tonekabon, Iran. Email: kia_esm@yahoo.com.